Technical Field

The present invention relates to a skateboard, and more particularly, to an all- direction running skateboard capable of freely moving, such as moving forward and backward in addition to a right and a left, as well as rotating in place.

Background Art

Generally, a skateboard includes a footplate and a wheel attached to the footplate and two wheels forming a pair and are fastened to a front portion and a rear portion of the footplate, respectively. Since pairs of wheels attached to a front and a rear are disposed parallel to each other and fastened without pivoting ability, a direction may be changed by controlling a centroid, to change the direction while riding a skateboard. Accordingly, a radius for turning becomes very large and a wide space for the turn has to be provided.

Also, since it is difficult to generate driving force itself for a general skateboard, a user has to kick the ground while riding on a flat surface.

To solve the described disadvantage, an improved skateboard such as a snake board is disclosed. To consider the snake board and boards similar to the snake board, a user is on separated footplates and alternately moves both feet, thereby obtaining a driving force. However, the snake board and the similar boards only progress in the directions of right and left of a body and are not easy to rotate in a narrow space due to a considerable radius required for turning. Also, it is difficult to stop the snake board by itself on a downhill, and it is impossible to adjust a length of the snake board to suit a height of the user.

Namely, though the improved skateboard such as the snake board may obtain a driving force by itself by alternately leaning on each foot, since only one wheel is used for each footplate, it is difficult to stand on the snake board in a natural stance, it is impossible to get on the snake board while kicking the ground or running, when requiring rapid acceleration, and it is difficult to stop by itself on an inclined place. Due to one long body connected by a fixed axis, a radius of turning is large when performing a 360 degree rotation or making a U-turn while driving. Since the user has

to maintain a specific posture and a position of a foot when getting on the snake board, body motion is restricted and is not free. Above all, since a progressive direction cannot vary, there are many restrictions on available activities.

Disclosure of Invention Technical Goals

An aspect of the present invention provides a skateboard capable of moving forward and backward in addition to a right and a left of a user.

An aspect of the present invention also provides a skateboard capable of variously changing a posture and position of footplates according to conditions.

An aspect of the present invention also provides a skateboard capable of easily controlling an interval between footplates according to a body of a user and automatically expanding and contracting the interval between footplates.

An aspect of the present invention also provides a skateboard capable of stably stopping and easily controlling speed while driving on an incline or in a hazardous situation.

Technical Solutions

According to an aspect of the present invention, there is provided a skateboard including: a central rod unit; a first footplate installed to an end of the central rod unit to be rotatable on a vertical axis; a plurality of first casters installed to be rotatable, independent from the first footplate; a second footplate installed to another end of the central rod unit to be rotatable on another vertical axis; and a plurality of second casters installed to be rotatable, independent from the second footplate. Since the first and second footplates are installed on both ends of the central rod unit on the vertical axis, it is easy to rotate right and left and a desired foot shape position may be maintained when a user reposes or drives. For example, the user may dispose the footplates in the shape of H interposing the central rod unit therebetween to move right and left or forward and backward. Also, the user may closely attach the footplates to both sides of the central rod unit to enable a progressive direction to be identical with a direction of feet. In addition, the user may dispose both feet in the shape of a T, to be parallel to each other, and may maintain the both feet in the shape of

V. In this case, since the casters below the footplates freely rotate by 360 degrees or freely rotates in a certain range, the user may easily maintain a driving state though a posture of the user does not have to be identical with the progressive direction.

Also, the footplates may rotate right and left with respect to the central rod unit, and the footplates may be additionally designed to rotate or twist on a horizontal axis and/or a longitudinal axis of the central rod unit. Namely, the footplates may rotate up and down on a vertical axis and a horizontal axis vertical to the longitudinal axis on the both ends of the central rod unit. Also, the footplates may twist on the longitudinal axis of the central rod unit. Also, the footplates may rotate on the horizontal axis and the longitudinal axis, and may have a restoring force to return to an original position against the rotation and the twist so that the user can stably use the skateboard.

According to another aspect of the present invention, there is provided a skateboard including: a central rod unit; two footplates installed to both ends of the central rod unit to be rotatable; elastic supporters disposed at bottoms of the footplates, respectively, and including a suspension supporting a bottom surface of the footplates; and a plurality of directional casters installed to the elastic supporters to be independently rotatable, respectively.

The elastic supporters are installed between the footplates and the directional casters. Though the footplates are generally maintained to be parallel to a top surface of the directional caster, a partial bend between the footplates and the top surface of the directional caster may be generated by the elastic supporter while driving. Accordingly, the user may easily keep his or her balance to safely maintain a centroid and may easily change a direction, and an impact transferred from the ground may be effectively excluded. The directional caster rotates in a position where a caster wheel is biased based on a turning axis by a bearing. Accordingly, the caster wheel of the directional caster rotates in a position biased opposite to a progressive direction, and the position may be changed in response to a direction of the skateboard.

Also, since the directional caster is disposed below the elastic supporter, the caster wheel is biased opposite to the progressive direction and the suspension of the elastic supporter is inclined to the caster wheel. Since the elastic supporter is biased to the caster wheel, the directional casters of the one footplate substantially tends to be in

one direction and the user may obtain a desired driving force by alternating both feet.

According to still another aspect of the present invention, there is provided a skateboard including: a central rod unit formed in a double pipe structure capable of elastically expanding and contracting lengthwise; two footplates installed on both ends of the central rod unit; and a plurality of casters installed to the respective footplate and elastically bending. In detail, the two footplates may be installed to rotate on a vertical axis and a horizontal axis on both sides of the central rod unit, respectively, and may twist in a certain boundary angle range on a longitudinal axis of the central rod unit. In this case, the footplates have a restoring force to return to an original position by receiving a restoring force of a spring while pivoting on the horizontal axis and vertical axis, and twisting on the longitudinal axis.

Also, at least one caster is installed to the respective footplate. For example, two or more casters may be installed to the both footplates. However, in this case, one caster may be installed to one footplate and two casters may be installed to the other footplate. The respective caster includes at least one footplate fixture installed on a bottom surface of each of the footplates to be rotatable, an elastic connecting portion connected to a bottom of the footplate fixture and bending in a predetermined range, a wheel connecting portion installed on a bottom of the elastic connecting portion to be rotatable, and a caster wheel installed to the wheel connecting portion to be rotatable. A directional caster rotating in a position biased against a pivot axis of the footplate fixture may be used as the caster wheel.

The elastic connecting portion of the respective caster may bend in a direction opposite to a progressive direction. The casters in the same footplate substantially tend to be in the same direction. Accordingly, a user may obtain a desired driving force by alternating each foot and may advance forward and backward as well as right and left of a body. Accordingly, the user may go forward by moving as when walking.

The plurality of casters may each turn in a different direction. The plurality of casters is disposed on a concentric circle structure and may rotate by 360 degrees in place. Also, the footplate may rotate up and down by 20 degrees, respectively, in a total of 40 degrees, on the horizontal axis and may twist 25 degrees in both directions, respectively, in a total of 50 degrees, on the longitudinal axis. Also, since the footplate is limited to rotate right and left by 90 degrees, in a total of 180 degrees, on the vertical

axis, convenience of the user may be improved.

The user may make a board in the shape of I — I by using the described skateboard. Also, the skateboard may be adjusted to be suitable for a height of the user by extending or taking in the central rod unit. The skateboard may be variously transformed by rotating one or two of the footplates in the shape of I, right or left. Also, the skateboard may be driven by moving or pushing the footplates forwards or backwards. When driving on a downhill or at high speed, the user can change a direction by leaning and riding on an edge, as in a snowboard riding, and can reduce a speed by pressing a brake.

Brief Description of Drawings

FIG. 1 is a bottom perspective view illustrating a skateboard according to a first embodiment of the present invention;

FIG. 2 is a side view illustrating the skateboard of FIG. 1; FIG. 3 is a front view illustrating the skateboard of FIG. 1;

FIG. 4 is a partial enlarged view illustrating a caster 150 of FIG. 1;

FIG. 5 is a partial enlarged view illustrating another caster similar to the caster of FIG. 4;

FIG. 6 is a perspective view illustrating a skateboard according to a second embodiment of the present invention;

FIG. 7 is a perspective view illustrating another state of the skateboard of FIG. 6;

FIG. 8 is a perspective view illustrating still another state of the skateboard of FIG. 6; FIG. 9 is a side view illustrating the skateboard of FIG. 6;

FIG. 10 is a top view illustrating the skateboard of FIG. 6 rotating in place;

FIG. 11 is an enlarged side view illustrating a skateboard according to a third embodiment of the present invention;

FIG. 12 is an enlarged side view illustrating the skateboard of FIG. 11 in a state of progress;

FIG. 13 is an enlarged side view illustrating another state of progress of the skateboard of FIG. 11;

FIG. 14 is an enlarged side view illustrating a skateboard according to another embodiment similar to the third embodiment of the present invention; and

FIG. 15 is an enlarged side view illustrating a skateboard according to still another embodiment similar to the third embodiment of the present invention.

Best Mode for Carrying Out the Invention

Hereinafter, the exemplary embodiments of the present invention will be described in detail with reference to the attached drawings. However, the present invention is not limited or defined by the embodiments. Embodiment 1

FIG. 1 is a bottom perspective view illustrating a skateboard according to a first embodiment of the present invention, FIG. 2 is a side view illustrating the skateboard of FIG. 1, and FIG. 3 is a front view illustrating the skateboard of FIG. 1.

Referring to FIGS. 1 through 3, a skateboard 100 includes a central rod unit 110, footplates 120, elastic supporters 140, and casters 150, which are installed to both ends of the central rod unit 110. Two footplates 120 are installed to the both ends of the central rod unit 110 to be rotatable right and left. The elastic supporters 140 including suspensions 142 are provided below the footplates 120. Since the two suspensions 142 support the footplate 120 at both sides of the elastic supporter 140, right and left movement of a user may be transferred to the casters 150 via the footplates 120. Also, the caster 150 is fastened to be unidirectionally biased and may rotate below the elastic supporter 140 by 360 degrees or a limited range of less than 360 degrees.

The central rod unit 110 has a duplex structure. Namely, a central cylinder 112 that is hollow is provided, and sliding rods 114 are inserted into both sides of the central cylinder 112. The sliding rods 114 may move along an inner hole and may mutually move lengthwise to the central cylinder 112.

Also, a tension spring 116 is provided between the sliding rods 114. The tension spring 116 is coupled with an inner end of the sliding rod 114 and pulls the sliding rod 114 inwardly. Though the tension spring 116 is used in the present embodiment, according to other embodiments of the present invention, a compression spring may be interposed to provide repulsive force to push a sliding rod or a spring is installed between both ends of a central cylinder and an inner end of a sliding rod to

provide repulsive force to push the sliding rod inwardly.

Referring to FIGS. 1 through 3, a rotational joint 132 is installed to the both ends of the central rod unit 110. The rotational joint 132 is for connecting the central rod unit 110 to the footplate 120 and the footplate 120 can rotate and twist with respect to the central rod unit 110 by the rotational joint 132. The rotational joint 132 is installed to an end of the sliding rod 114 and may rotate on a longitudinal axis X of the central rod unit 112. In this case, a torsion spring may be installed between the central rod cylinder 112 and the rotational joint 132, and a restoring force may be continuously provided by using the torsion spring so that the rotational joint 132 may return to an original position.

A hole vertically penetrating the rotational joint 132 is formed, and a hole vertically penetrating an elevation joint 134 installed to the footplate 120 is formed. The rotational joint 132 may be coupled with the elevation joint 134 by a vertically penetrating pin and may rotate on the pin. Similarly, a pin hole penetrating the elevation joint 134 from a right and a left is formed, and the elevation joint 134 is installed to the footplate 120 to vertically rotate.

Similar to the central cylinder 112 and the rotational joint 132, a torsion spring may be installed between the rotational joint 132 and the elevation joint 134, and a torsion spring may be installed between the elevation joint 134 and the footplate 120. Each of the joints may have a restoring force to maintain an original position by the torsion spring. Therefore, a user may maintain a stable posture while freely moving both feet.

Though different depending upon a situation, the rotational joint 132 may bidirectionally twist in a boundary angle range of less than approximately 25 degrees on the longitudinal axis X of the central rod unit 110. In this case, the boundary angle range may be controlled to be an angle of 25 degrees or less, depending upon an intention of a designer. The footplate 120 may bidirectionally rotate vertically in a boundary angle range of less than approximately 20 degrees on a horizontal axis Z around the rotational joint 132 and may rotate in both right and left directions in a boundary angle range of less than approximately 90 degrees on a vertical axis Y.

Though the central rod unit 110 has a structure elastically expanding and contracting in the present embodiment, depending upon a situation, the central rod unit

110 may be fastened to the sliding rod 114 by a pin or other fixtures. This may be applied or used by a selection of the designer or the user, and the user may fix a length of the central rod unit 110 to suit a body of the user.

Referring to FIG. 2, the caster 150 includes a wheel 156, and the wheel 156 includes a wheel connecting portion 154 unidirectionally biased with respect to a rotation axis W of the caster 150. The caster 150 includes a footplate fixture 152 including a bearing, the wheel connecting portion 154 formed below the footplate fixture 152, and the wheel 156. Since the wheel 156 is unidirectionally biased, the wheel 156 is disposed opposite to a progressive direction of the caster 150. Since a position of the wheel 156 is passively determined by the progressive direction of the caster 150, a movement of the caster 150 and the skateboard 100 is not disturbed. Also, since each of two casters 150 connected to one footplate 120 independently rotate, movements of the two casters 150 do not interfere with each other.

FIG. 4 is a partial enlarged view illustrating the caster 150 of FIG. 1. Referring to FIG. 4, a wheel brake 158 is installed to the caster 150. The wheel brake 158 is installed between the caster 150 and the elastic supporter 140 and has a structure capable of vertically rotating. Accordingly, when the user pushes a rear portion of the footplate 120 to tilt the footplate 120 and the elastic supporter 140 backwardly, a bottom of the wheel brake 158 may touch the ground and may generate a resisting force. The user may use a part or an entirety of the wheel brake 158 of the footplate installed on a front and a rear of the skateboard 100 to stop or to control a speed of the skateboard 100.

FIG. 5 is a partial enlarged view illustrating another caster similar to the caster of FIG. 4. Referring to FIG. 5, a wheel brake 159 also has a structure capable of vertically moving. However, friction surface of the wheel brake 159 is with an outer circumferential surface of the wheel 156 instead of the ground. The user may closely make contact with the wheel brake 159 to the wheel 156 by tilting the footplate 120. The wheel brakes 158 and 159 shown in FIGS. 4 and 5 may be applied to the skateboard 100, respectively, and may be used together with each other.

Referring to FIGS. 2 and 3, the suspension 142 may be formed of a compression spring or an elastic material capable of being used in an identical manner

as the compression spring and may be disposed on either side between the elastic supporter 140 and the footplate 120 to support right and left tilting of the user. The suspension 142 may be vertically compressed and may bend towards the right and left or front and back. The user may naturally control the tilt right and left and the tilt front and back by the suspension 142. For example, the user may operate the wheel brake 158 by tilting the footplate 120 opposite to the progressive direction. The wheel brake 158 is fastened to a top of the wheel 156 and is connected to pivot at a certain angle.

Embodiment 2 FIG. 6 is a perspective view illustrating a skateboard according to a second embodiment of the present invention, and FIG. 7 is a perspective view illustrating another state of the skateboard of FIG. 6.

Referring to FIGS. 6 and 7, a skateboard 200 includes a central rod unit 210, footplates 220 installed to both ends of the central rod unit 210, and casters 250. Two footplates 220 are installed to the both ends of the central rod unit 210 to rotate right and left, and the casters 250 are provided below the footplates 220. Each caster 250 is a directional caster unidirectionally biased and may independently rotate below the footplate 220. A range of the rotation may be variously controlled to be 360 degrees or a limited range of less than 360 degrees. Similar to the first embodiment, the central rod unit 210 has a duplex structure.

Namely, a central cylinder 212 that is hollow is provided, and sliding rods are inserted into both sides of the central cylinder 212 (refer to 214 of FIG. 9). The sliding rods may move along an inner cavity of the central cylinder 212, respectively, and may mutually move in a direction of a length of the central cylinder 212. Also, a tension spring is provided between the sliding rods. The tension spring is coupled with an inner end of the sliding rod and pulls the sliding rod inwardly.

As illustrated, a central footplate 218 is installed above the central rod unit 210. The central footplate 218 may be used for temporarily putting a foot on and may protect the central rod unit 210. Rotational joints 232 are installed to the both ends of the central rod unit 210, respectively. The rotational joint 232 is for connecting the central rod unit 210 with the footplate 220. The footplate 220 can rotate and twist with respect to the central rod

unit 210. The rotational joint 232 is installed to an end of the sliding rod and may twist on a longitudinal axis X of the central rod unit 210. In this case, a torsion spring may be additionally installed between the central cylinder 212 and the rotational joint 232 and a restoring force may be continuously provided so that the rotational joint 232 may return to an original position by using the torsion spring.

Also, a hole vertically penetrating the rotational joint 232 is formed, and a hole vertically penetrating a connecting joint 234 installed to the footplate 220 is formed.

The rotational joint 232 and the connecting joint 234 may be coupled with each other by a pin vertically penetrating the rotation joint 232 and the connecting joint 234 to rotate on it.

Similar to the central cylinder 212 and the rotational joint 232, a torsion spring may be installed between the rotational joint 232 and the connecting joint 234. Each of the joints may have a restoring force to return to an original position by the torsion spring. Accordingly, the user may maintain a stable posture while elastically moving both feet.

Referring to FIG. 6, the footplates 220 are disposed perpendicular to and on right and left sides of the central rod unit 210. Also, four casters 250 are disposed parallel to the longitudinal axis X of the central rod unit 210. This corresponds to when the user puts his or her feet parallel to each other and moves in right or left directions of the user's body.

Referring to FIG. 7, the footplates 220 are disposed lengthwise, parallel to each other on both sides of the central rod unit 210. However, in this case, the four casters

250 are disposed parallel to the longitudinal axis X of the central rod unit 210, which corresponds to when the user put his or her feet parallel to a progressive direction and moves forward.

In this case, for example, the user may dispose both footplates in the shape of T by vertically disposing his or her right foot sideways to the progressive direction, to be vertical to his or her left foot disposed in a front and may dispose the footplates in the shape of V by inwardly drawing heels of both feet. In any case, the casters 250 may become oriented parallel to the progressive direction and the user may maintain a comfortable posture.

Also, though not shown, the user may install a binding device for fixing both

feet or one foot to a footplate. The binding device may strongly bind the foot with the footplate, and various binding devices such as a strong binding device used for a snowboard or a simple binding device easily securing and releasing the foot may be used. FIG. 8 is a perspective view illustrating still another state of the skateboard of

FIG. 6, and FIG. 9 is a side view illustrating the skateboard of FIG. 6.

Referring to FIG. 8, the user may put the both feet on the footplate 220 and may move forward. The user may move the right foot forwardly by using the left foot as an axis, and the footplate 220 may move forward together with the right foot. In this case, the casters 250 are disposed parallel to the progressive direction, and the user may alternately move each foot forward similar to walking.

Referring to FIG. 9, in the present embodiment, the central rod unit 210 has the duplex structure, and a length of the central rod unit 210 may be extended and contracted while a sliding rod 214 slides in the central cylinder 212. Particularly, as shown in FIG. 8, the right footplate 220 moves forward and the central rod unit 210 is extended more than the original length, thereby easily moving forward.

Also, a tension spring 216 may be installed between the sliding rods 214 so that the central rod unit 210 may return to the original length. The tension spring 216 is coupled with inner ends of the sliding rods 214 to pull the sliding rods 214 inwardly after the sliding rods 214 are extended, thereby enabling the central rod unit 210 to be short again without the user directly pulling the sliding rods 214. Generally, since the operation of spreading and swinging legs is easy and the operation of putting the legs together is difficult and unnatural, swinging of the legs may be naturally performed by using the tension spring 216. Referring to FIG. 9, the caster 250 includes the wheel 256, and the wheel 256 includes the wheel connecting portion 254 unidirectionally biased with respect to the rotation axis W of the caster 250. The caster 250 includes a footplate fixture 252 including a bearing, the wheel connecting portion 254 formed below the footplate fixture 252, and the wheel 256. Since the wheel 256 is unidirectionally biased, the wheel 256 is disposed opposite to a progressive direction of the caster 250. Since a position of the wheel 256 is passively determined by the progressive direction of the caster 250, a movement of the caster 250 and the skateboard 200 do not interfere with

each other. Also, since each of the two casters 250 connected to a single footplate 220 independently rotate, movements of the two casters 250 do not interfere with each other.

FIG. 10 is a top view illustrating the skateboard of FIG. 6 rotating in place.

Referring to FIG. 10, the central rod unit 210 and the footplate 220 are disposed in the shape of an H, and four casters 250 are disposed toward a direction to rotate in place. Accordingly, the casters 250 may rotate on a point where rotation axes of the wheels 256 are gathered. Also, a rotation of 360 degrees in place may be performed, which is impossible by conventional skateboards or similar products. Accordingly, the skateboard 200 according to the present embodiment may perform relatively sharp turns and may stop by using rotation, similar to a roller skate. This is possible because each of the casters 250 can independently rotate and is impossible to embody in a conventional skateboard whose two wheels are fixed to be parallel to each other or a snake board whose two wheels are disposed in one line.

Referring to FIG. 9, the wheel brake 258 is installed to the caster 250. The wheel brake 258 is installed to the wheel connecting portion 254 by interposing the rotation axis of the wheel 256 therebetween and has a structure capable of vertically rotating. Accordingly, when the user pushes a rear portion of the footplate 220 to tilt the footplate 220, a bottom of the wheel brake 258 may touch the ground and may generate a resisting force. The user may use a part or an entirety of the wheel brake 258 of the footplate installed in the front and the rear to stop the skateboard 200 or to control speed of the skateboard 200.

Embodiment 3

FIG. 11 is an enlarged side view illustrating a skateboard according to a third embodiment of the present invention, and FIG. 12 is an enlarged side view illustrating the skateboard of FIG. 11 in a state of progress.

Referring to FIGS. 11 and 12, a skateboard 300 includes a central rod unit 310, footplates 320 installed to both ends of the central rod unit 310, and a plurality of casters 350. Two footplates 320 are installed to the both ends of the central rod unit 310 to rotate right and left, and the plurality of casters 350 are provided below the footplates 320. Each caster 350 is a directional caster unidirectionally biased and may independently rotate below the footplate 320. A range of the rotation may be variously

controlled to be 360 degrees or a limited range of less than 360 degrees.

Rotational joints 332 are installed to the both ends of the central rod unit 310, respectively. The rotational joint 332 is for connecting the central rod unit 310 with the footplate 320. The footplate 320 has a degree of freedom to rotate and twist with respect to the central rod unit 310. The rotational joint 332 is installed to an end of the sliding rod 314 and may twist on a longitudinal axis of the central rod unit 310. In this case, a torsion spring may be additionally installed between the central cylinder 312 and the rotational joint 332, and a restoring force may be continuously provided so that the rotational joint 332 may return to an original position by using the torsion spring. Also, a hole vertically penetrating the rotational joint 332 is formed, and a hole vertically penetrating a connecting joint 334 installed to the footplate 320 is formed. The rotational joint 332 and the connecting joint 334 may be coupled with each other by a pin vertically penetrating the rotation joint 332 and the connecting joint 334, and may rotate on the pin. The caster 350 is installed below the footplate 320 and includes a footplate fixture 352, an elastic connecting portion 353, a wheel connecting portion 354, a wheel 356, and a wheel brake 358. The wheel 356 is installed to the wheel connecting portion 354 and is unidirectionally biased with respect to a rotation axis W of the caster 350. The footplate fixture 352 includes a bearing and may rotate 360 degrees or in a limited range of less than 360 degrees with respect to the footplate 320. The elastic connecting portion 353 including a spring is provided below the footplate fixture 352. Since a position of the wheel 356 is passively determined by the progressive direction of the caster 350, a movement of the caster 350 and the skateboard 300 do not interfere with each other. Also, since each of two casters 350 connected to one footplate 320 independently rotates, movements of the two casters 350 do not interfere with each other.

The caster 350 freely rotates regardless of other casters to provide a sufficient driving force in a progressive direction, but in actually may interfere with forward progress. Accordingly, via the elastic connecting portion 353, the caster 350 may bend opposite to a progressive direction of the caster 350 and the plurality of casters 350 may be substantially disposed to be parallel to the progressive direction by slightly limiting a rotation of the caster 350. Accordingly, the user may obtain a desired driving force by

alternating each foot and may move forward and backward as well as right and left of the user's body. Accordingly, the user may move forward by moving as when walking. In this case, though the wheel connecting portion 354 also includes a bearing and may rotate 360 degrees or in a limited range of less than 360 degrees with respect to the elastic connecting portion 353, since rotation is limited when the elastic connecting portion 353 bends, the wheel connecting portion 354 only rotates right and left in a certain range.

FIG. 13 is an enlarged side view illustrating another state of progress of the skateboard of FIG. 11. Referring to FIG. 13, as shown in FIG. 8, the user may move forward, and the casters 350 may bend opposite to the progressive direction while the user moves forward. Accordingly, the user may get a sufficient driving force when moving forward instead of moving right and left.

Accordingly, the user may move forward while putting both feet on each respective footplate 320. The user may advance the right foot by using the left foot as an axis, and the footplate 320 may also move forward together with the right foot. In this case, the casters 350 are disposed parallel to the progressive direction, and the user may alternate advancing each foot as when walking.

A wheel brake may be installed to the caster 350. Particularly, the wheel brake may be installed to the wheel connecting portion 354 by interposing the rotation axis of the wheel 356 therebetween and has a structure capable of vertically rotating. Accordingly, when the user pushes a rear portion of the footplate 320 to tilt the footplate 320, a bottom of the wheel brake 358 may touch the ground and may generate a resisting force. The user may use a part or an entirety of the wheel brake of the footplate 320 installed in a front and a rear to stop the skateboard 300 or to control a speed of the skateboard 300.

In addition, a movement direction of the skateboard 300 may be different according to where the user puts a centroid or a direction of force. Namely, according to the centroid or the direction of force, a direction of a directional caster may be changed and may rotate by at most 90 degrees horizontally to a central rod unit and a movement of a footplate may apply elasticity to the speed of the skateboard 300.

Also, when the user turns the user's body around a center of both footplates,

each of the directional casters tends to move outwardly due to centrifugal force, thereby rotating 360 degrees in place. The user may go downhill by positioning both feet and the body right or left and may rotate forming a circle while inwardly drawing heels to the body and tilting the body backwardly. Also, when the user makes the shape of T by twisting one foot by 90 degrees while standing straight up, it is easy to go over an obstacle or a curb between a road and a sidewalk.

FIG. 14 is an enlarged side view illustrating a skateboard according to another embodiment similar to the third embodiment of the present invention.

Referring to FIG. 14, the skateboard includes the central rod unit 310, the footplates 320 installed to both ends of the central rod unit 310, and the casters 351. Two footplates 320 are installed to the both ends of the central rod unit 310 to rotate right and left, and the casters 351 are provided below the footplates 320. The caster 351 is a directional caster unidirectionally biased and may independently rotate below the footplate 320. A range of the rotation may be variously controlled to be 360 degrees or a limited range of less than 360 degrees. The rotational joint 332, the central cylinder 312, and the sliding rod 314 may be described with reference to the description and the drawings of the previous embodiments.

The caster 351 is installed below the footplate 320 and includes the footplate fixture 352, the elastic connecting portion 353, the wheel connecting portion 354, the wheel 356, and the wheel brake 358. Only, unlike the previous embodiment, there is no bearing between the wheel connecting portion 335 and the elastic connecting portion 353. Accordingly, the footplate fixture 352 including the bearing may rotate 360 degrees or in a limited range of less than 360 degrees, and the wheel connecting portion 355 has rotation ability relatively more limited than the elastic connecting portion 353. Depending upon another embodiment, an elastic connecting portion may be twisted or deformed itself, thereby giving rotation ability in a limited range.

Since a position of the wheel 356 is passively determined by the progressive direction of the caster 351, a movement of the caster 351 and the skateboard 300 do not interfere with each other. Also, since each of the two casters 351 connected to one footplate 320 independently rotates, movements of the two casters 351 do not interfere with each other. Though limited rotation ability of the wheel connecting portion 355 may limit free rotation of the skateboard 300, a sufficient driving force with respect to

the progressive direction may be provided. Via the elastic connecting portion 353, the caster 351 may bend opposite to a movement direction of the caster 351. A driving force generated by the casters 351 may be improved by slightly limiting rotation of the casters 351. FIG. 15 is an enlarged side view illustrating a skateboard according to still another embodiment similar to the third embodiment of the present invention.

Referring to FIG. 15, the skateboard includes the central rod unit 310, the footplates 320 installed to both ends of the central rod unit 310, and casters 350'. Two footplates 320 are installed to the both ends of the central rod unit 310 to rotate right and left, and the casters 350' are provided below the footplates 320. The caster 350' is a directional caster unidirectionally biased and may independently rotate below the footplate 320. A range of the rotation may be variously controlled to be 360 degrees or a limited range of less than 360 degrees. The rotational joint 332, the central cylinder 312, and the sliding rod 314 may be described with reference to the description and the drawings of the previous embodiments.

The caster 350' is installed below the footplate 320 and includes the footplate fixture 352, an inclined connecting portion 353', the wheel connecting portion 354, the wheel 356, and the wheel brake 358. However, unlike the previous embodiment, the inclined connecting portion 353' has a top surface and a bottom surface not parallel to each other but inclined to each other. Accordingly, when a spring is not used, the wheel connecting portion 354 and the wheel 356 are already bending respective to the footplate 320. However, the inclined connecting portion 353' may rotate by being connected to the footplate fixture 352 and the wheel connecting portion 354, respectively. In the present embodiment, since a position of the wheel 356 is passively determined by the progressive direction of the caster 350', a movement of the caster 350' and the skateboard 300 does not interfere with each other. Also, since each of the two casters 350' connected to one footplate 320 independently rotates, movements of the two casters 350' do not interfere with each other. Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these

embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Industrial Applicability The skateboard according to an exemplary embodiment of the present invention may move forward and backward as well as right and left of a user by generating a sufficient driving force and has three or four casters independently rotating to reduce a turn radius.

Also, since a footplate may move toward a direction different from a direction of a caster while driving, a direction of the footplate may be easily changed. For example, it is possible to enjoy boarding in various positions in the shapes of H, II, T, and V. Also, convenience of the user may be improved by maintaining a comfortable boarding posture.

Also, an interval between footplates may be easily adjusted to suit a physical body of the user. Particularly, the interval between the footplates may be reduced in the operation of moving forward as when walking, thereby naturally moving forward.

Also, when going downhill or in a hazardous situation, the skateboard may safely stop, speed of the skateboard may be easily controlled, and it is easy to avoid a hazard by easily turning.